1. Field of the Invention
The present invention relates to electrical transfer switches used, for example, to disconnect from a first circuit and connect to a second circuit, and is used in the transmission and distribution of power over the grid and within industrial and commercial facilities. It addresses the need for very fast power transfers in emergency situations such as power failures and malfunctions, and to short circuit or arcing conditions to reduce electrocutions, burns and injury due to arc flash, explosions and noise, and damage to equipment and infrastructure.
2. Related Art
Conventional power transfer switches generally comprise two types, electromechanical and solid state. Solid state power transfer switches require 2-4 ms (milliseconds) to effect a circuit transfer. Electromechanical power transfer switches typically require 4 to 10 cycles (67 to 167 ms). Electromechanical devices such as power transfer switches are almost universally used. The Bureau of Labor Statistics reports that there is a yearly average of 290 fatalities from electrocution, more that 4,000 disabling injuries and 3,600 non-disabling injuries. A major cause is the slow response of electromechanical safety devices. Solid state power transfer switches are very expensive and simply blow protective fuses when the short circuit current rise times are too fast. The proposed transfer switch is expected to have circuit transfer time of a few hundred microseconds (e.g. 0.2 ms). This is ten times faster than solid state power transfer switches and over three hundred times faster than electromechanical power transfer switches. This fast transfer time reduces personnel exposure to the long time constant of potentially fatal current flows. Furthermore, arcs remain, for “a few milliseconds” at the arcing points before developing and expanding out to endanger personnel. The few hundred microsecond transfer time into a load dump can prevent the arc from enlarging thereby minimizing or eliminating burns and injuries due to arc flash, explosions and noise as well as damage to equipment. Fast interception of the arc current can reduce the probability of electrocution.